Hybridization, fertility and herbicide resistance of hybrids between wheat and Aegilops biuncialis

Genetically modified crops are now grown worldwide and their area of cultivation is increasing yearly. Although transgenic crops offer benefits, several risks have been identified associated with their cultivation. One such risk is their potential for hybridization with wild species, and weed-related species, and the possible escape and subsequent introgression of the transgenes into these species. Transgenic wheat varieties are being successfully developed and field-tested, primarily on herbicide-tolerant wheat. If genetically modified herbicide-tolerant wheat is commercialized in the near future this may result in the escape of the inserted gene from the crop and its incorporation into closely related wild species. This fact could give a competitive advantage to the recipients. For risk assessment purposes it is necessary to determine the frequency of crop-wild transgene flow and the fertility of hybrids. Most wheat-wild hybridization studies have been conducted with the purpose of breeding with wheat acting as the female parent in crosses, but very limited information is available focused on hybrid production with wheat as the male parent. Here, we studied (1) the potential hybridization between wheat and the wild related Aegilops biuncialis, and (2) the fertility of the hybrids. Hybridization was quantified in crossing experiments over 5 years in a greenhouse using three wheat cultivars as pollen donors and emasculated plants of one A. biuncialis population as pollen recipients. Hybridization was estimated as the ratio of number of seeds set to the number of flowers pollinated in percentage terms. Our results show that hybrids between wheat and A. biuncialis are formed easily, with hybridization rates ranging from 8.5 to 75%. The fertility of the hybrids, measured as the number of seeds per spikelet (%), was also evaluated by self-pollination and by backcrossing. Most of the hybrids were self-sterile but 11 F seeds were obtained from 191 A. biuncialis-wheat hybrids. However, backcrossing seeds were found in all BC combinations at average rates of 3.7% (0-19.6%) for greenhouse experiments, and 4.6% (0-28.9%) for field experiments. In subsequent generations, although few plants were available, BCF exhibited a certain degree of fertility, up to 3.57% with the cultivar Chinese Spring. F and BC were also checked for resistance to the herbicide difenzoquat that was present in the parental wheat, while A. biuncialis was susceptible. Difenzoquat resistance was maintained in the F hybrids and also in the derived BC plants. This information on hybridization and fertility of the first A. biuncialis-wheat hybrid generations could be an initial step to assess the relative advantage of hybridization in the adaptive ability of A. biuncialis and hybrid derivatives and the impact thereof on the environment and agricultural system. This needs to be studied in depth when wheat and A. biuncialis share habitat. © 2008 INRA EDP Sciences.